QUESTION

Can I install tile over my 24" o.c. floor? - I did have a general question about a tile job I am considering for my sunroom. It measures 12 by 24 and the space below is finished so I can’t access the joist. The situation I am running into is the space between the joist. This house was built 7 years ago and since I selected a vinyl floor, the builder placed my joist 24 inches on center. The builder has recommended hardwood over tile for the job but thought a 3/8 or ½ inch piece of plywood with Ditra on top would also suffice.

My local tile shop is pushing hardy backer. (Room is climate controlled and fully finished) My question- Is tile even a good idea for this situation and if so, what would you recommend. I am looking at a standard 12 by 12 ceramic tile.

ANSWER

ANSWER - It is definitely a good idea.  If you have a sun room then you want to have cementitious material under the tile in order to take advantage of the energy savings from the passive solar benefits of tile and concrete substrates.  I'm not a big fan of ditra, but in some cases it might work.  I do believe they do allow for 24" o.c. spacing.  1/2" hard backer board might work, but you will have to check their data sheets.  I think they only allow 19.2" spacing.

There are 24" o.c. joist methods that are recommended.  You can apply a 3/8" exterior-glue laminated birch wood panel with a minimum of 7 piles over a 23/32" t & g exterior-glue plywood per TCNA F160 and bond directly to it.  The key is not to have excessive deflection which would be more than L/360.  You have a relatively small area so depending on how the floor was constructed and braced it might meet that.  You need to make sure you have movement joints along the perimeter of the room to allow for movement within the tile assembly.  Those joints can be left open and covered by a base board or tile, or you can fill them with a silicone or urethane sealant that meets ASTM C920.  good luck.